Wave guide attenuator



June 17, 1952 BOWEN 2,600,466

WAVE GUIDE ATTENUATOR Filed May 7, 1945 //v VENTOR- A. E. BOWEN I?" BY?Arrouzv Patented June 17, 1952 UNITED STATES PATENT WlAVE GUIDEATTENUATOR Arnold E. Bowen, Red Bank, N. J., assignor to. BellTelephoneLaboratories, Incorporated, New York, N. Y., av corporation ofNew York Application May 7, 1943, Serial No. 486,013

21 Claims. 1

This invention relates to wave transmission network and moreparticularly to an attenuator for guided electromagnetic waves.

An object of the invention is to attenuate guided electromagnetic waves.

Another object is to provide a wave guide attenuator which may becontinuously varied from zero to any chosen upper limit of attentuation.

In transmission systems employing an airfilled metallic pipe as a guidefor electromagnetic waves it is often desired to introduce a knownamount of attenuation. It is convenient to be able to vary theattenuation continuously from zero to the required upper limit.

The present invention provides a wave guide attenuator which iscontinuously variable from zero to any desired maximum value. Theattenuator comprises a section of metallic pipe wave guide within whichis longitudinally positioned a resistive septum. To make the attenuatorvvariable, means are provided for moving the septum sidewise and therebyvarying the separation between the septum and a side of the waveguide.In the embodiment disclosed the guide is of rectangular cross-sectionand the septum is parallel to a side of the section.

The nature of the invention will be more fully understood from thefollowing detaileddescription and by reference to the accompanyingdraw,- ings in which:

Fig. 1 is a perspective vview of a wave guide attenuator in accordancewith the invention;

Fig. 2 is a plan view, partly in section, of the attenuator of Fig. 1;and

Fig. 3 is. a perspective view of theresistive septum used in theattenuator shown in Figs. 1 and 2.

As shown in perspective in Fig. 1 and in plan in Fig. 2, the attenuatorcomprises a section of metallic pipe wave guide I of rectangularcross-section, a resistive septum 2 positioned within the section Isubstantially parallel to the shorter dimensioned side 3 of the sectionI and means for moving the septum 2 either toward or away from the side3. Each end of the section I is provided with a flange 4 for connectingthe attenuator to an adjacent section ofwave guide. The flange 4 may beprovided with aligning pins 5 which fit into holes such as 6 in a flangeon the end of the adjacent section of, guide. They section I is made ofa metal or an alloy having good electrical conductivity such, forexample, as brass, and is preferably plated on the inside with preciousmetal such, for example, as silver or platinum.

The septum 2 is moved by means of a rod I to the inner endof which theseptum 2 is fastened by a screw 8 which passes through a cen tral holein-the-septum2 and screwsinto a tapped hole in the end of the rod I. Therod1= and the screw 8 are madeof suitable insulating material such, forexample, as hard rubber. The rod? 1 slides in a hole 9-in the lowerblock I0 and: passes through a hole II in the side 3 ofthe guide sectionI. The rod I is actuated by means of the rack I2-, which is fastenedtothe rod I, and the pinion'gear I3. The pinion I3-.is on the lower end ofa shaft I4 which passes through a hole in the upper block I5. and isheld in. place by the pronged member l6 which is fastened at one end tothe top of the block I5 andat the other end fits into an annulargroove-in the shaft; I4. The upper-block I5'is fastened to the lowerblock III by the screws I1 and the entire assembly is securely attachedto the side 3 of the section. I.

The dial I8 and knob I9: are fastened tothe upper end of the shaft I4 bythe setscrew20-and a pointer orindex 2|, fastened tothe section I; isprovided for reading the calibration on the dial I8, as shown at 22. Thecalibration 22 may conveniently be made directly in decibels.

As shown more clearly in the perspective view of Fig. 3, the septum 2-consists of a plate of suitable insulating materialsuch, for example, asphenol fibre, coated on the face toward the side 3 with one or morelayers of resistive material 23. The resistive material may, forexample,be a mixture of finely divided graphite and-a suit.- able binder,sprayed onto the side ofrthe septum 2 in one or more coats. Theendsofrthe septum 2 are preferably specially. shapedto reduce. thereflection effects when the section lis inserted into the wave guidesystem. Asv shown at 24 and 25 in Fig. 3, this special shaping mayxtakethe form of' arectangular notch, the optimum depth and-width ofwhicharebest determined by trial. Other forms of special shaping may,however, be used. In order to minimize. the variation inattenuation withfrequency the central'hole' 26 in the septum 2 may be extended on eachside in the longitudinal direction, as shown at 21 and 28. The optimumdimensions for these extensions are also best found by trial.

The amount of attenuation introduced by the attenuator depends primarilyupon the length, width and thickness of the-resistive coating" 23 andthe distance between the septum 2 and the side 3 of the section I. Whenthe septum 2 is in contact with the side 3 the attenuation issubstantially zero. As the septum 2 is moved away from the side 3 theattenuation increases in accordance with a smooth curve until a maximumis reached when the septum 2 has moved half-way or less across thesection I. The desired attenuation is obtained by turning the knob l9which rotates the pinion gear [3 and, acting through the rack 12, pushesthe rod 1 either in or out and thus determines the separation betweenthe side 3 and the septum 2, which is fastened to the end of the rod 1.A maximum attenuation of as high as 40 decibels has been obtained with avariable attenuator of the type disclosed herein.

What is claimed is:

1. An attenuator comprising a section of metallic pipe wave guide and aresistive septum longitudinally positioned within said section andspaced from a side of said section, the ends of said septum beingnotched.

2. An attenuator in accordance with claim 1 in which the ends of saidseptum have rectangular notches.

3. An attenuator comprising a section of metallic pipe wave guide ofrectangular cross-section and a resistive septum positioned within saidsection substantially parallel to, but separated from, a side of saidsection, the ends of said septum being notched.

4. An attenuator in accordance with claim 3 in which the ends of saidseptum have rectangular notches.

5. A variable attenuator comprising a section of metallic pipe waveguide, a resistive septum longitudinally positioned within said sectionand means for moving said septum laterally.

6. An attenuator in accordance with claim 5 in which the ends of saidseptum are notched.

7. An attenuator in accordance with claim 5 in which said septumcomprises a Plate 0f insulating material coated on a major face with resistive material.

8. A variable attenuator comprising a section of metallic pipe waveguide of rectangular crosssection, a resistive septum positioned withinsaid section substantially parallel to a side of said section and meansfor moving said septum laterally.

9. An attenuator in accordance with claim 8 in which said septumcomprises a plate of insulating material coated on a major face withresistive material.

10. An attenuator in accordance with claim 8 in which said section hasunequal cross-sectional dimensions and said septum. is substantiallyparallel to a side of said section having the shorter width dimension.

11. An attenuator in accordance with claim 8 in which said means permitmoving said septum to a position of substantially zero attenuation.

12. An attenuator in accordance with claim 8 in which said means permitmoving said septum from a position of substantially zero attenuation toa position of maximum attenuation.

13. An attenuator for use in a wave guide in which high frequencyelectric waves are propagated comprising a wave guide portion having amode of propagation in which the maximum intensity electric vector liesin a flat plane symmetrically through and longitudinal of said guideportion, a thin, flat resistance member carried by said guide sectionandhaving an effective portion thereof lying in a plane parallel to themaxi- 4 mum intensity electric vector and means for moving saideffective portion from a region of minimum electric field intensity to aregion of maximum electric field intensity whereby a continuouslyvariable degree of attenuation may be provided.

14. An attenuator in accordance with claim 5 in which one end of saidseptum is specially shaped to reduce reflection.

15. An attenuator in accordance with claim 8 in which one end of saidseptum is specially shaped to reduce reflection.

16. A variable attenuator comprising a section of metallic pipe waveguide, a resistive septum longitudinally positioned within said sectionand means for moving said septum laterally, in which the ends of saidseptum are specially shaped to reduce reflection.

17. A variable attenuator comprising a section of metallic pipe waveguide of rectangular crosssection, a resistive septum positioned withinsaid section substantially parallel to a side of said section and meansfor moving said septum laterally, in which the ends of said septum arespecially shaped to reduce reflection.

18. A variable attenuator comprising a section of metallic pipe waveguide of rectangular crosssection, a resistive septum positioned withinsaid section substantially parallel to a side of said section and meansfor moving said septum laterally, in which said means permit moving saidseptum from a position adjacent to a side of said section to a positionapproximately half-way across said section.

19. An attenuator for a rectangular wave guide comprising a relativelythin plate of dielectric material carrying on at least one broad facethereof a loss-producing coating, said plate being mounted within saidguide with its plan parallel with the electric field in said wave guide,and means at one end of said plate for matching the input impedance ofsaid attenuator to the characteristic impedance of said wave guide.

20. An attenuator comprising a section of metallic pipe wave conductor,an elongated dielectric carrier longitudinally positioned within saidsection, a coating of resistive material on the main section of saidcarrier, and at least one end portion of said carrier having a resistivecoating of a different resistance value per unit length of the carrierthan the coating on said main section to reduce wave reflection in saidconductor.

21. An attenuator comprising a section of metallic pipe wave conductor,an elongated dielectric carrier longitudinally positioned within saidsection, a coating of resistive material on th main section of saidcarrier, and at least one end portion of said carrier having a resistivecoating specially shaped to reduce wave reflection in said conductor.

ARNOLD E. BOWEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,151,157 Schelkunofi Mar. 21,1939 2,207,845 Wolfi July 1 6, 1940

